2.6. Total polyphenol
Total polyphenols of flour obtained from three non-commercial
banana cultivars was determined using the Folin–Ciocalteu colorimetric
methods. The method is based on the reduction of MoO4+ to
MoO3+ that is detected by colour change from yellow to blue; measured
at 760 nm. Approximately 0.2 g of milled sample was weight
and 2 mL of acetone was added to the milled sample. The mixture
was incubated for 1 h at room temperature, shaking occasionally
and centrifuged at 6000 rpm for 5 min at 4 C. To 9 lL of centrifuged
sample in a microplate, 109 lL of Folin Ciocalteu solution
was added. About 180 lL of 7.5% Na2CO3 was added to the mixture,
covered with aluminium foil and incubated at 50 C for 5 min.
Absorbance of samples was then read at 760 nm using a UV spectrophotometer
microplate reader (Zenyth 200rt Biochrom, UK).
Gallic acid was used as the standard phenol compound and acetone
used as the extraction solvent. The results were expressed as
equivalents of gallic acid (mg GAE/100 g d.w.) from the calibration
curve.